1. Field of the Invention
The present invention relates to a gray scale display (or gradation display) control device for controlling gradational display to be made on the screen of a display apparatus (or unit), such as a liquid crystal display apparatus, for performing binary (level) display.
2. Description of the Related Art
Generally, a frame thinning (out) method has been known as a method of performing gradational display on the screen of a liquid crystal display apparatus. This method is to divide a plurality of picture elements (namely, pixels) into groups (or clusters) by setting each of the clusters as consisting of, for example, 4*4 pixels (namely, 16 pixels) and to further make "pixel groups", which are arranged (or established) over a plurality of groups of pixels, correspond to gradation (or tone) levels, respectively, and to cause the "pixel groups" to blink every frame.
Multi-gray-scale (or multi-tone-level) display system based on such a frame thinning method is disclosed in Japanese Unexamined Patent Publication No. 1-225997. In accordance with this multi-gray-scale display system, as viewed in FIG. 10, pixels arranged in a matrix on the screen of a display apparatus are partitioned into groups (namely, clusters) so that each cluster consists of 16 pixels arranged in a matrix having 4 columns (namely, 4 pixels arranged in the X-direction (or the lateral direction)) and 4 rows (namely, 4 pixels arranged in the Y-direction (or the vertical or upward (or downward) direction)). Further, "pixel groups" P00 to P33 are set in such a manner as to correspond to pixels of each cluster, respectively. Moreover, lighting/non-lighting (status) signals, namely, blink signals, which respectively correspond to tone levels, are supplied to these "pixel groups" every frame, so that one screen picture representing a 16-gray scale display is constituted by 16 frames.
The number of times of changing the status of each of the "pixel groups" P00 to P33 between the lighting status and the non-lighting status, namely, that of times of blinking corresponding thereto varies with a corresponding gray scale (namely, to a corresponding tone level). In the case of an example utilizing the 16-gray scale display, when the gray scale is K0 in which a screenful white picture is displayed on the screen of the display apparatus, the number of frames, in which each of the "pixel groups" is lighted, among 16 frames is 0. This is indicated by a duty (cycle or factor) of 0/16. Further, when the gray scale is KF in which a screenful black picture is displayed on the screen of the display apparatus, the number of frames, in which each of the "pixel groups" is lighted, among 16 frames is 16. Namely, all through the 16 frames, the "pixel groups" are turned on (or lighted). This is indicated by a duty (cycle or factor) of 16/16. When the gray scale is within halftone gray scales (or levels) K1 to KE, the duty ranges from 2/16 to 15/16.
FIG. 11 is a diagram showing the display condition or mode of each of the "pixel groups" P00 to P33 in each frame in the case of, for example, the gray scale K1. In this figure, a high level (corresponding to a data value "1") of a data signal indicates that a corresponding "pixel group" is in a lighting status. Further, a low level (corresponding to a data value "0") of a data signal indicates that a corresponding "pixel group" is in a non-lighting status. As is seen from this figure, in the case that the gray scale is K1, namely, the duty is 2/16, the "pixel group" P00 is lighted up in a first frame F0 and a ninth frame F8. Further, a "pixel group" P01 is lighted up in a fifth frame F4 and a thirteenth frame FC. As shown in the rest of FIG. 11, the other "pixel groups" are similarly lighted up twice. Moreover, the display conditions or modes of all pixels of one group (or cluster) will be checked hereinbelow correspondingly to each frame. As shown in (1) of FIG. 12, the "pixel groups" P00 and P22 are lighted up in the first frame F0. Further, as shown in (2) of FIG. 12, the "pixel groups" P02 and P20 are lighted up in the second frame. Thereafter, similarly, the "pixel groups" P11 and P33 as lighted up in the third frame F2; and the "pixel groups" P13 and P31 in the forth frame F3, as illustrated in (3) and (4) of FIG. 12. Incidentally, the lighting condition or status of each of the "pixel groups" in the case of the gray scale K2 is illustrated in FIG. 13. Furthermore, the lighting condition or status of each of the "pixel groups" in the case of the gray scale K3 is illustrated in FIG. 14. However, the description of such conditions of the "pixel groups" is omitted for simplicity of description.
Further, the blinking conditions of the "pixel groups" (namely, "pixel groups" to be lighted up in the frames, respectively) are determined according to data preliminarily written to storage means (for instance, a shift register), which is provided in a conventional gray scale display control device, correspondingly to each gray scale.
The individual "pixel groups" P00 to P33 of each of groups partitioned in this manner are adapted in such a way as to be randomly selected and blinked every frame so that flickers are thereby prevented from being caused on the screen of a display apparatus. Moreover, such "pixel groups" P00 to P33 are adapted so that brightness (or luminance) changes respectively caused in the groups (or clusters) obtained by partitioning pixels are completely uniformed by synthesizing the blinking condition of each of such groups from those of the "pix groups" P00 to P33 corresponding to each gray scale. However, observers' feelings toward flickers varies with the blink rate of the pixels on the screen of the display apparatus and with unevenness in the distribution of (the positions of) the blinking (namely, lighting/non-lighting) pixels in each of the groups (or clusters). Therefore, if flickers occur in a specific gray scale (or tone level), the conventional gray scale display control device cannot reduce the flickers.